- on one's own account
- on one's own time
- on one's part
- on one's say-so
- on one's shoulders
- on one's soapbox
- on one's tail
- on one's toes
- on one's uppers
- on one's way
- on oneself
- on order
- on pain of
- on paper
- on pins and needles
- on principle
- on purpose
- on record
- on relief
- on request
- on sale
- on schedule
- on second thought
- on sight
- on someone's
- on someone's back
- on someone's coattails
- on someone's nerves
- on someone's side
- on speaking terms
- on spec
- on standby
- on strike
- on sufferance
- on tap
- on target
- on tenterhooks
- on the Hill
- on the Q.T.
- on the air
- on the alert
- on the average
- on the ball, be
- on the bandwagon, get
- on the barrel
- on the beam
- on the bench
- on the blink
- on the block
- on the brain
- on the bum
- on the button
- on the carpet
- on the chance that
- on the cheap
- on the chin
- on the contrary
- on the cuff
- on the defensive
- on the dot
- on the double
- on the edge
- on the eve of
- on the face of it
- on the fence, be
- on the fly
- on the fritz
- on the go
- on the heels of
- on the horizon
- on the horns of a dilemma
- on the hour
- on the house
- on the in, be
- on the increase
- on the inside
- on the job
- on the lam
- on the level
- on the line
- on the lines of
- on the lookout
- on the loose
- on the make
- on the map
- on the mark
- on the market
- on the mend
- on the money
- on the move
- on the nail
- on the nose
- on the off chance
- on the one hand
- on the order of
- on the other foot
- on the other hand
- on the outs
- on the part of
- on the point of
- on the prowl
- on the qui vive
- on the rack
- on the rebound
- on the receiving end
- on the right foot, get off
- on the right tack
- on the road
- on the rocks
- on the ropes
- on the run
- on the safe side
- on the same wavelength
- on the scene, be
- on the shelf
- on the side
- on the side of the angels
- on the sidelines
- on the skids
- on the sly
- on the spot
- on the spur of the moment
- on the square
- on the street
- on the strength of
- on the surface
- on the table
- on the take
- on the tip of one's tongue
- on the town
- on the up-and-up
- on the uptake
- on the verge of
- on the wagon
- on the warpath
- on the watch
- on the way
- on the way out
- on the whole
- on the wing
- on the wrong foot
- on the wrong side of bed
- on the wrong tack
- on thin ice
- on time
- on tiptoe
- on to
- on top
- on top of
- on top of the world
- on trial
- on view
- on welfare
- on your life
- on, be
- on-again, off-again
- on-air
- on-camera
- on-glide
- on-limits
- on-message
- on-mike
- on-off
- on-peak
- on-ramp
- on-record
- on-screen
- on-seam
- on-season
- on-site
- on-stream
- on-target
- on-the-job
- on-the-record
- on-the-scene
- on-the-spot
- on-trend
- onager
- onagraceous
- onanism
- onanist
- onanistic
- onbeat
- onboard
- onboarding
- once
- once and for all
- once bitten, twice shy
- once in a blue moon
- once in a lifetime
- once in a while
- once over lightly
- once upon a time
- once-over
- once-over-lightly
- oncer
- onchocerciasis
- oncidium
- onco-
- oncogene
- oncogenesis
- oncogenic
- oncogenicity
- oncolite
- oncology
- oncoming
- oncornavirus
- oncost
- ondes Martenot
- ondine
- onding
- ondograph
- one
- one and all
- one and only
- one and the same
- one another
- one by one
- one eye on
- one fell swoop, in
- one foot in the grave, have
- one for the books
- one for the road
- one good turn deserves another
- one in a million
- one jump ahead
- one man's meat is another man's poison
- one of a kind
- one of these days
- one of those days
- one old cat
- one on one
- one on, that's
- one picture is worth a thousand words
- one that loved not wisely but too well
- one up
- one way or another
- one-a-cat
- one-acter
- one-armed bandit
- one-bagger
- one-base hit
- one-dimensional
- one-down
- one-drop rule
- one-eighty
- one-eyed
- one-handed
- one-horse
- one-horse town
- one-legged
- one-liner
- one-lung
- one-lunger
- one-man
- one-man show
- one-many
- one-night stand
- one-nighter
- one-note
- one-off
- one-on-one
- one-one
- one-parent family
- one-piece
- one-reeler
- one-shot
- one-sided
- one-size-fits-all
- one-spot
- one-star
- one-step
- one-stop
- one-suiter
- one-tailed
- one-time
- one-to-one
- one-track
- one-track mind
- one-trick pony
- one-two
- one-up
- one-upmanship
- one-way
- one-way mirror
- one-way ticket
- one-woman
- one-worlder
- onefold
- oneiric
- oneiro-
- oneirocritic
- oneirocriticism
- oneiromancy
- oneness
- oner
- onerous
- oneself
- onesie
- oneˈ-upmanship